That thing about Mysql

Optimization summary:

1. full value match
2. optimal left prefix rule
3. Don't do calculations on the index
4. The column to the right of the range condition is invalid
5. Try to use covering index to reduce select *
6. Do not use inequality on index fields
7. Do not judge null on the index field
8. The index field uses like and does not start with a wildcard
9. Index field strings should be enclosed in single quotes
10. Do not use or for index fields